NAPA, Calif. — Residents of this picturesque wine-making area north of San Francisco have been warned to be careful around buildings damaged by a weekend magnitude-6.0 quake because of the danger of aftershocks that could continue for several weeks.

The quake struck early Sunday about 6 miles south of Napa, according to the U.S. Geological Survey.

It was the largest to shake the San Francisco Bay area since the magnitude-6.9 Loma Prieta quake struck in 1989, collapsing part of the Bay Bridge roadway and killing more than 60 people, most when an Oakland freeway fell.

At least 172 people were treated Sunday for injuries at a hospital, and three were in critical condition.

One of the most serious cases was a child who was airlifted to UC Davis Medical Center in Sacramento, the San Francisco Chronicle reports. The boy had been hit by debris from a falling chimney. Also in critical condition were a person who suffered a heart attack and another with a broken hip.

The quake, which knocked out power to thousands of people and hit the wine-making industry on the eve of its harvest, could result in more than $100 million in losses.

In addition, Pacific Gas & Electric, which serves the quake-hit area, says it will be looking for possible gas leaks in the coming days.

PG&G says it has received hundreds of calls from people reporting the smell of gas since the quake struck and that 20 customers remained without gas Monday morning.

Guests in the five-story Andaz Napa hotel, one of the tallest structures in the city, were immediately evacuated, many remaining on n the sidewalk, with their luggage, even hours later, wondering about alternative accommodations, the Napa Valley Register reports.

One guest, Cheryllyn Tallman, told the newspaper that she was so shaken she planned to cut short her wine country vacation and head back home to the East Coast.

"I live in Upstate New York," Tallman said. "We just have blizzards — and they tell you when they are coming."

Gov. Jerry Brown declared a state of emergency for Napa, Solano and Sonoma counties. Schools in Napa Valley were ordered closed Monday.

By midday Sunday, fires — including one that destroyed four homes at a mobile home park — were out and power was starting to be restored, said Mark Ghilarducci, director of the California Governor's Office of Emergency Services.

Rubble that fell from the Vintner's Collective tasting room on Main Street lays on the sidewalk after a 6.0 earthquake struck the Napa Valley area. The building has been red-tagged, which means no one can enter until officials inspect the structure.
Monica Davey, European Pressphoto Agency

Elvira Balbazar, an employee at the 3J's Oriental Market, cleans up after an earthquake on Aug. 24 in American Canyon, Calif. A large earthquake caused significant damage in California's northern Bay area, igniting fires and sending at least 87 people to a hospital.
Rich Pedroncelli, AP

A room at The Alexandria Square building crumbled during an earthquake in Napa, Calif. Officials in the city of Napa say 15 to 16 buildings are no longer inhabitable after the magnitude-6.0 earthquake.
Noah Berger, AP

It took several people to move one of the aisle shelves back into place at the Ranch Market in Napa, Calif, after the earthquake. It was one of few stores open for business near downtown Napa after the 6.0 earthquake rocked the area.
Jessica Brandi Lifland for USA Today

Hannah Housley, the owner of Ranch Market, takes an order at the door of her store near downtown Napa after the earthquake. The Ranch Market was selling items at the door until the store was cleaned up enough to be open properly for business.
Jessica Brandi Lifland for USA Today

Guests who evacuated their rooms at the Andaz hotel in Napa, wait for a ride to another hotel after their hotel suffered moderate damage in the magnitude-6.0 earthquake.
Peter DaSilva, European Pressphoto Agency

A truck navigates around a buckled section of California's Highway 12 after a magnitude-6.0 earthquake hit the San Francisco Bay Area at 3:20 a.m. PT near Sonoma, Calif., on Aug. 24.
Peter DaSilva, European Pressphoto Agency

A California Highway Patrol officer redirects traffic from a buckled section of California's Highway 12 after a magnitude-6.0 earthquake hit the San Francisco Bay Area on Aug. 24.
Peter DaSilva, European Pressphoto Agency

"While it was bad, it wasn't as bad as it could be and it was very manageable from a regional perspective," Ghilarducci said.

Residents, however, were bracing for aftershocks that usually follow big temblors.

On Sunday night in Southern California, a small, magnitude-3.3 earthquake hit off the region's coast. The U.S. Geological Survey said the temblor struck at 7:50 p.m. and was centered about 5 miles southwest of San Pedro and 6 miles southeast of Rancho Palos Verdes. There were no initial reports of damage, police said.

State geologist John Parrish said the aftershocks will decrease in magnitude and that it is unlikely there would be a large follow-up earthquake. Still, he warned people to be careful because newly damaged buildings are now more susceptible to collapse from aftershocks.

About 15 buildings were damaged too severely to allow people inside, and many more awaited further evaluation. Ghilarducci said 90 to 100 homes and buildings were deemed uninhabitable.

Wine and olive oil bottlers suffered damage. Hundreds of broken bottles littered the floor of Lucero Olive Oil, but owner David Gadlin said the store would reopen Monday as usual.

"A lot of downtown business owners will be back up and running," he said. "There's been financial hardship, but we'll get through it. Few people were hurt. That's what's important."

Lou Ishaq said at a service station he owns that he had a major cleanup job and had to get a battery from Sacramento, but managed to start pumping gas again.

"I think we'll recover pretty quick,'' he said. "The people who sustained major structural damage will have the worst of it. But everyone else, it's just clean up, assess your losses and get going."

Bertha Flores, 40, was out buying ice to keep the food in her refrigerator cold as her family waited for the power to come back on.

Speaking in Spanish, she said the earthquake frightened her children, but everyone was OK except for some cuts from shattered glass.

"I'm a cleaner. I think there is going to be a lot of work for my company in the next couple of days,'' she said.